This invention relates to electric resistance heating elements, and more particularly, to plastic insulated resistance heating elements containing encapsulated resistance material.
Single heating element fluid heaters tend to develop a temperature cycle where the temperature of the heated fluid repeatedly varies between a maximum and a minimum temperature over a period of time. The fluid is initially heated to the maximum temperature, at which point the heating element of the fluid heater is deactivated. The fluid then loses heat do to radiant and convective cooling. The fluid heater is designed to reactivate the heating element when the temperature of the fluid falls below a selected minimum temperature, at which point the fluid is again heated to the selected maximum temperature. The temperature cycle then repeats itself.
Because the fluid heater typically includes a single large wattage heat source that is capable of quickly heating the fluid from an ambient temperature or below to the desired elevated temperature, the constant cycle of switching the large wattage heat element xe2x80x9conxe2x80x9d and xe2x80x9coffxe2x80x9d is quite electrically inefficient as well as damaging to the high wattage heating element. This problem was recognized in U.S. Pat. No. 5,703,998 to Charles M. Eckman, entitled xe2x80x9cHot water tank assembly,xe2x80x9d issued Dec. 30, 1997, the entirety of which is hereby incorporated by reference herein.
Eckman ""988 discloses a hot water heater having a first and second resistance wires. Both wires are activated to initially heat the water to at least the temperature of a hot beverage. Once this temperature is reached, the first resistance wire is deactivated, and the second resistance wire remains energized to maintain the water at the hot beverage temperature. The heating element of Eckman ""988 includes a resistance heating coil surrounded by a corrosive resistant sheath. The sheath and the coil are insulated from each other by an insulating medium, such as a powdered ceramic material.
A single length of resistance wire coated with a polymeric layer has also been proposed as a fluid heater, such as in U.S. Pat. No. 4,326,121 to Welsby et al., entitled xe2x80x9cElectric immersion heater for heating corrosive liquids,xe2x80x9d issued Apr. 20, 1982, the entirety of which is hereby incorporated herein by reference. Welsby et al. ""121 discloses an electric immersion heater having a planar construction which contains an electrical resistance heating wire shrouded within an integral layer of polymeric material, such as PFA or PTFE, which is wound around end portions of a rectangular frame. The frame and wound resistance wire are then secured in spaced relationship with one or more wrapped frame members, and then further protected by polymeric cover plates which allow for the free flow of fluid through the heater.
While Welsby et al. ""121 illustrates one possible application for a polymeric coated resistance heating wire, and Eckman ""988 provides an approach to counteract the inefficiencies of temperature cycling inherent in fluid heaters containing single large wattage heating elements, neither reference accounts for heat losses that may occur downstream from the primary fluid heat source, e.g., in a piping section in fluid communication with an output of the primary heat source for the fluid. Further, neither reference provides a retrofitable solution to this problem.
As an example, a typical hot beverage vending machine, such as a coffee, tea or hot chocolate vending machine, contains a primary fluid heat source and a length of piping that connects the primary heat source to a dispensing outlet for the beverage. If the machine is in constant use, the temperatures of the beverages dispensed from the machine all fall within a fairly consistent and acceptable range, i.e., the beverage does not remain within the piping section leading to the dispensing outlet long enough to cool to a temperature below an acceptable temperature. If the machine is in disuse for any lengthy period of time however, such as for a few hours or overnight, any beverage contained in the piping section loses an unacceptable amount of its heat and is generally non-potable. These cold beverages are typically discarded. Over the life of the machine, this wasteful practice can amount to significant lost revenues.
Therefore, there remains a need for a heater that is capable of heating a fluid downstream from a primary heat source, thereby eliminating the wasteful discarding of unheated products all while doing so in an energy efficient manner. Still further, is desirable to be able to retrofit this functionality into existing heating applications in a capital and labor efficient manner.
The present invention provides a heater for maintaining a fluid substantially at a desired use temperature while said fluid is disposed in a section of piping disposed in fluid communication with an output of a primary heat source for the fluid that initially heats the fluid to at least the desired use temperature. The heater comprises a resistance heating element comprising a resistance heating wire having a pair of terminal ends connected to a pair of electrical connectors. The resistance heating wire is encapsulated within a thin electrically insulating polymeric layer. The resistance heating wire is capable of maintaining the fluid substantially at the desired use temperature. A heater includes a first connecting body configured to be coupled to the section of piping and including a first fluid inlet port, a first fluid outlet port, a first electrical connection port and a first fluid passageway defined between the first fluid inlet port and the first fluid outlet port. The resistance heating element is disposed at least partially within the first fluid passageway, and at least a first one of the terminal ends is coupled to a respective one of the electrical connectors through the first electrical connection port.
The heater of the present invention allows for efficient heating of a fluid downstream from a primary fluid heat source in order to maintain the desired use temperature of the fluid. The heater eliminates the need to reheat the fluid after it has lost a significant portion of its heat and/or the need to discard the cooled fluid. The heater may be easily retrofitted into existing fluid heating applications, particularly where downstream heating is desirable but had not previously been considered. Further, the heater is capable of utilizing existing pipe fittings and pipe fitting techniques.